Barn free

'THE threat certainly hasn't passed, but the future is probably brighter than it has been in nearly a century." Colin Shawyer, director of the Hawk and Owl Trust, is cautiously optimistic when he looks at the prospects for Britain's favourite raptor.

Barn owls: during the 1930s there were about 12,000 pairs in Britain, now there are around 4,400

Until recently, barn owls seemed to be in an inexorable, slow decline. During the 1930s there were about 12,000 pairs, but the loss of rough pasture and nest sites, coupled with pesticides and increased motor traffic, had reduced numbers to 3,800 by the early 1990s. Matters were not helped by the fact that, in Britain, the owls are at the northernmost limit of their range, and a series of bad winters in the late 1970s and early 1980s hit them hard.

Now the slide appears to have been halted; the latest estimates put the population at 4,400 pairs and the Trust is hoping for 6,000 by 2015.

One of the main causes of this change in fortunes has been the Trust's nest box scheme. Despite their name, barn owls prefer hollow trees to buildings for nesting, but both are in short supply. "Dutch elm disease and increased worries about human safety mean that large trees with dustbin-size cavities are dwindling," says Shawyer. "Meanwhile, conversions of old farm buildings mean there are less of these around, too."

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The answer is to fit specially designed, tea-chest-sized nest boxes to isolated trees and the outside of barn buildings. "The more obvious the better," Shawyer says. "They're not very good at finding boxes inside buildings."

Barn owl factsScientific name: Tyto alba.Description: Britain's only pale medium-sized owl (7oz/200g), yellow-brown on the back, but usually with an almost pure white underside.Distribution: found across Europe, Asia, Africa and Australasia. In Britain, most common in East Anglia, parts of Sussex, Wiltshire, Somerset, Lancashire and south-west Scotland. Rare above 600ft/200m.Population: around 4,400 pairs.Habits: often seen quartering over rough, tussocky grassland at dawn and dusk, but still surprisingly elusive.Diet: almost exclusively small rodents.Breeding: one or two clutches of three to eight eggs are laid each year in a disused building or dustbin-sized tree hollow. The eggs hatch sequentially and the youngest (and smallest) often fail to survive the nine weeks until they leave the nest.

The owls are taking rapid advantage of the new opportunities. "Someone was interrupted by a mobile phone call when putting up a box," says Chris Mead, of the British Trust for Ornithology. "When he came back for his ladder an owl was already inside."

Overall, 85 per cent of the Trust's 1,000 boxes show signs of use, although landowners are frequently oblivious to their presence. "It's surprising how often I visit 'unused' boxes in farmyards to be greeted by five owlets," Shawyer says. "You'd have thought that a medium-sized white bird that hunts by slowly quartering fields would be obvious, but they can be incredibly elusive." The most reliable way to detect their presence is listening for their snoring calls.

Increased productivity is another surprising benefit: "Providing two boxes seems to encourage double-clutching," says Shawyer. Barn owls do this naturally, but because of the young's long period of dependency (a month's incubation and then nine weeks before fledging), there is usually no room in the original nest for the female to incubate a second clutch. "Laying on more nest sites could be one of the best ways of speeding up the current recovery," he says.

Not that all attempts at help have been so successful. "I had a friend who arrived in the car park of a National Trust reserve to see someone releasing two owls from the back of his car," says Mead. "He boasted that he'd bred and released 400 in six years." Unfortunately, such well-meaning actions usually end in tragedy. Barn owls are comparatively slow to mature, spending nine weeks in the nest, and are reliant on their parents for top-up feeds as they learn to hunt. Without careful monitoring and help, captive-bred birds struggle in the wild.

"Before any release, one needs to conduct a careful survey of the area and local barn owl population," Mead adds. "If there are no owls, there's probably a good reason, and if there are - and the incomers survive - they make life difficult for the existing birds."

Colin Shawyer agrees: "Not only is it usually pointless, but there are at least four subspecies of barn owl in captivity in Britain," he says. "If the South African strain were to start breeding with our native birds it would pose a genetic threat." As a result, releases are now illegal without a licence.

A much more productive approach is the provision of nest boxes, and even urban owl-lovers can provide practical help for the owls through the Trust's Adopt a Box scheme. Given nest sites and a suitable habitat, there seems a huge potential for reclaiming lost territory. "It's amazing how little land they need to hunt," says Mead. "Twenty acres can sustain a pair - they are incredibly efficient hunters." He cites a friend who watched one couple bring seven voles to the nest in just 25 minutes. In his own area of north Norfolk there are six pairs within two miles: "This is largely thanks to arable farming, which allows some tussocky grass along hedges. Shooting interests also help, because they see the value of a bit of rough pasture." In contrast, because sheep graze more closely, western and upland areas often lack the vital terrain.

There are other obstacles to recovery. As territorial birds, barn owls are very sedentary and can move only along corridors of suitable habitat. Roadside verges are one possibility but, unlike kestrels, their hunting technique of quartering back and forth makes these very unsafe. "I know one lorry driver who regularly reports 100 casualties a year," says Mead. "It's a tragedy, but it's very difficult to see how we can reduce the threat."

Engine noise is another problem for this vocal species, which communicates with low-frequency grunts. "Research suggests that any road with more than 60,000 traffic movements a day seriously hampers birds like barn owls by drowning out their calls," Mead says.

This leaves the owls struggling to link existing strongholds such as those in South Yorkshire and East Anglia. Rivers and canals are the natural answer. "We estimate that 85 per cent of Britain's barn owls are tied to lowland river valleys," Shawyer says. "It's here that our boxes are proving most successful and more of these could help populations join up and build on the beginnings of a recovery."

To find out how you can help, send an sae to The Hawk and Owl Trust, 41b Dartmouth Road, London NW2 4ET. Alternatively, visit the Trust's website at www.hawkandowl.co.uk.